It is generally known to form heat resistant fabrics of various types of yarns. For example, hazardous industrial work uniforms, firefighter uniforms, and military protective uniforms have been formed of fabrics fabricated of yarns formed of non-synthetic fibers, such as cotton or wool. These fabrics are then topically treated with conventional halogen-based and/or phosphorous-based fire retarding chemicals. However, uniforms formed of this type of fabric have a limited wear life, and are heavier in weight than non-flame retardant uniform fabrics, the chemical treatment typically adding about 15% to 20% to the weight of the fabric. When this type of fabric is burned, it forms brittle chars which break away with movement of the fabric.
Also, it is known to form fire resistant garments of fabrics fabricated of yarns formed entirely of nonburning or high temperature resistant fibers or blends of nonburning fibers, such as Nomex, Kevlar or PBI. These fabrics do exhibit thermal stability but are very expensive to produce, and do not have the comfort, moisture absorbency, and dyeability characteristics of fabrics formed of natural fiber yarns.
U.S. Pat. Nos. 4,381,639; 4,500,593; and 4,670,327 disclose yarns for forming heat resistant fabrics which include a core of continuous glass filaments covered by a layer of heat-resisting aramid fibers. However, the yarns and fabrics disclosed in these patents are very expensive to produce because of the high cost of the fibers required to produce these yarns and fabrics. Also, the yarns and fabrics disclosed in these patents have the surface characteristics of the aramid fibers so that these fabrics do not have the desirable surface characteristics of dyeability and comfort of fabrics formed of conventional natural fibers, such as cotton, wool or the like.
U.S. Pat. No. 4,331,729 discloses a heat resistant fabric formed of a yarn including a core of carbon filaments and a cover of aramid fibers. The yarn and heat resistant fabric disclosed in this patent also includes the same type of disadvantages as pointed out in the above discussion of prior art patents.